lkml.org 
[lkml]   [2008]   [Nov]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] Enforce valid shift values in clocksource_register()
From
Date
On Thu, 2008-11-27 at 01:08 +0100, Thomas Gleixner wrote:
> On Wed, 26 Nov 2008, John Stultz wrote:
>
> > Thomas noted that some of the timekeeping core assumes
> > clocksource shift values will be less then 32. However,
> > we do nothing to enforce such limits.
> >
> > This patch prints a warning if a clocksource with an invalid
> > shift value is attempted to be registered, and will refuse to
> > register the clocksource
> >
> > I could not find any clocksources that use 32 or higher for a
> > shift value, so this should be only a preventive warning for
> > future clocksource writers.
> >
> > Signed-off-by: John Stultz <johnstul@us.ibm.com>
> >
> > diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
> > index 9ed2eec..4a3bb13 100644
> > --- a/kernel/time/clocksource.c
> > +++ b/kernel/time/clocksource.c
> > @@ -318,7 +318,7 @@ static int clocksource_enqueue(struct clocksource *c)
> > * clocksource_register - Used to install new clocksources
> > * @t: clocksource to be registered
> > *
> > - * Returns -EBUSY if registration fails, zero otherwise.
> > + * Returns -EBUSY or -EINVAL if registration fails, zero otherwise.
> > */
> > int clocksource_register(struct clocksource *c)
> > {
> > @@ -327,7 +327,14 @@ int clocksource_register(struct clocksource *c)
> >
> > /* save mult_orig on registration */
> > c->mult_orig = c->mult;
> > -
> > + if (c->shift >= 32) {
> > + printk(KERN_WARNING "===============================\n");
> > + printk(KERN_WARNING "WARNING: Cannot register %s clocksource\n",
> > + c->name);
> > + printk(KERN_WARNING "The shift value must be less then 32\n");
> > + printk(KERN_WARNING "===============================\n");
> > + return -EINVAL;
>
> Just setting the shift value to 31 along with a WARN_ON() should be
> enough. We don't need to kill the clocksource in that case, as this
> can be nasty when it happens in the early boot code where we dont have
> any output.

Well, we can't tweak the shift value without changing the mult. And that
seemed a bit overreaching (but might be safe). I'll give it a shot.

Also early boot we should have the jiffies clocksource around, so unless
I'm forgetting something, I don't think it has early boot concerns.

thanks
-john



\
 
 \ /
  Last update: 2008-11-27 01:49    [from the cache]
©2003-2011 Jasper Spaans